The U.S. Environmental Protection Agency (EPA) has taken a step toward requiring drilling companies to disclose chemicals used in hydraulic fracturing (fracking).

On Friday, the agency issued an advanced notice of proposed rulemaking (ANPR). A public comment period of 90 days will begin when the ANPR is published in the Federal Register, Law360 reports. The EPA is considering both mandatory and voluntary measures under the Toxic Substances Control Act (TSCA). “This mechanism could be regulatory (under TSCA Section 8(a) and/or Section 8(d)), voluntary, or a combination of both,” the agency notice said.

A coalition of environmental organizations including the Natural Resources Defense Council (NRDC) and Earthjustice petitioned the EPA in 2011 to issue TSCA rules that would require toxicity testing for fracking chemicals, and in July 2013, the EPA announced its intention to publish an ANPR. The EPA said it wants information about fracking chemicals “provided to the public in a transparent fashion,” according to the ANPR. Data that would have to be disclosed could include the identity and quantities of chemicals used, and the circumstances of use, as well as health and safety studies, according Law360.

Fracking is a drilling technique in which large amounts of highly pressurized water, sand, and chemicals are injected underground to fracture the shale layer and release oil and natural gas reserves. Fracking is controversial because it carries the risks of air, water, and soil contamination. According to the EPA, fracking makes heavy demands on the water supply, and companies must arrange for the safe disposal of the chemical-laced water.

The NRDC calls for full mandatory disclosure of fracking chemicals. An attorney for the organization argues, “For too long, the oil and gas industry has been allowed to keep their chemical cocktails a secret, while injecting them underground alongside drinking water sources, storing them in families’ backyards and transporting them through neighborhood streets,” according to Law360. “Even emergency room doctors have been refused answers necessary to treat patients who have been exposed to fracking chemicals,” he said.